Amoeba-doubling problem, help please

Hi everyone, I'm new to the forum. I'm taking an education course for math teachers. I got the following homework problem wrong, and the teacher won't tell me why. Please help. BTW, the teacher is awful, and everyone in the class got the same wrong-answer I did.

Verbatim: An amoeba is placed in a jar at 1PM. It reproduces by doubling every twenty minutes. How many amoebas will be in the jar just after 5PM that day?

Thanks. I agree that 4096 is correct. As to reading the problem more precisely, I ignore that there's no food for the amoebas, and that they might get overcrowded and perish from concussion, starvation, or cannibalism. Perhaps the amoeba is almost ready to split and becomes two the instant it hits the jar at 1pm. Doesn't seem cricket to assume that. Isn't this amoeba-doubling a standard math problem, which is designed specifically to teach that population=2^n, where n is the number of "gestation" periods and all progeny result from the single parent? Thanks.